


Ashen Demon

by LesbianDragon_LD



Category: Fire Emblem Series, Fire Emblem: Fuukasetsugetsu | Fire Emblem: Three Houses
Genre: Blood, Cunnilingus, Dom/sub Undertones, Edeleth, F/F, Vaginal Fingering, Vampires, because ofc there is blood on a vampire AU, even if they call her a demon it's a vampire basically, vampire!Byleth
Language: English
Status: Completed
Published: 2019-10-21
Updated: 2019-10-21
Packaged: 2020-12-27 21:50:11
Rating: Explicit
Warnings: No Archive Warnings Apply
Chapters: 1
Words: 3,098
Publisher: archiveofourown.org
Story URL: https://archiveofourown.org/works/21125798
Author URL: https://archiveofourown.org/users/LesbianDragon_LD/pseuds/LesbianDragon_LD
Summary: One night, Edelgard discovers by accident that Byleth's 'ashen demon' nickname has a more literal meaning than what people are aware of: her professor has a condition that makes her thirst for blood.She finds her professor weakened and distressed so Edelgard, of course, is more than eager to help.





	Ashen Demon

**Author's Note:**

> Idk guys, dom vampire!El is very hot and all but may my lesbian-wants-emperor-Edelgard-von-Hresvelg-to-step-on-her galaxy brain propose this 'Edelgard is so dom that as a mortal she can top a freaking vampire' AU instead?
> 
> Anyway, this is my main fic for the spook month! Happy Halloween guys (even if it's a bit early)!

Edelgard took a deep breath of fresh air before she turned back, walking back to her room. She knew students weren’t supposed to walk around the monastery at night, and yet she couldn’t help herself. It had been a rough night filled with nightmares, and she needed to feel the cool breeze on her face to compose herself. She had headed out towards the lake and after a few minutes of staring at the rippling water she had started to feel better, calm enough to return and try to get some sleep before morning came.  
So she walked back, but instead of turning and taking the closest set of stairs that lead to the second floor, she found herself wanting to check on professor Byleth. Lately, her professor had been looking more tired than usual and Edelgard just had a bad feeling about it on that particular night. She was already up after all, and walking towards professor Byleth’s room wasn’t that much of a detour anyway. She couldn’t stop thinking about it and before Edelgard had noticed it, her feet were walking on their own on the familiar trail that lead to her professor’s room.  
She arrived at her door and instantly felt silly for expecting anything to happen.  
Of course everyone was asleep, professor Byleth included.  
She could see no lights coming from any room and the only sound she could hear were crickets hiding in the near bushes.  
Why had she even expected anything else?  
Edelgard cursed herself and turned back to finally walk away. But before she could take a single step, she heard it;  
There was a loud thud, a sound that came from inside professor Byleth’s room.

“My teacher?” Edelgard immediately called out to the other side of the door, whispering loud enough to be heard by whoever was inside but not loud enough to wake the students next door.

When no one answered, she got closer to the door. She pressed her ear to it, only to hear heavy breathing and low growls, as if a wild animal was hurt inside the room. She feared the worst, and without hesitation she opened the door which was unlocked as if the professor was expecting someone.  
Edelgard finally entered and the darkness of the night prevented her from seeing professor Byleth fully. From the moonlight entering through the windows, she could only make out a figure lying on the floor, inches away from the bed as if it had fallen from it.  
Edelgard didn’t waste a single moment as she ran to help her professor.

“Dad…?” she heard Byleth call out as she kneeled beside her, holding her.

“No, my teacher, it’s Edelgard! What on earth happened?” she asked Byleth, the panic in her voice very clear as she tried to search the barely conscious professor for any wounds yet finding none. All she could see and feel was that her professor was alarmingly pale and cold…and then, Byleth opened her eyes.

Her eyes scared Edelgard.  
The usually dark blue irises were now colored with a pale blue shade that seemed to light up in the dark like a flame. And her pupils barely seemed human, looking like slits and resembling more a cat’s eyes than a person’s. Her eyes made her look like a beast.  
For a single moment, Edelgard was taken aback. She was confused, wondering if she was having a nightmare. But the more she stared at Byleth’s half open eyes, the more aware she became that it was all real.

“Y-you…have to…leave…” the weakened professor tried to command as she tried to pull away from Edelgard, but her strength failed her and she was unable to leave Edelgard’s arms.

Upon hearing her voice, Edelgard was pulled out of her trance.

“My teacher, I’m not leaving! I don’t know what’s wrong but I can take you to Manuela or-“

“N-no!” Byleth protested, “I can’t…I just need to wait for m-my father…please, you have to leave before I…I…”

Byleth’s voice died out and she fell eerily silent for a moment. Then, her eyes shot open, and Edelgard couldn’t help but yelp, confused by what was going on. She had never seen a condition like this before. Byleth’s eyes seemed to be focused on Edelgard now, the younger woman growing slightly concerned by how fixated they were on her. 

“Blood” Byleth let out in a strange voice, “please…blood…just a drip…”

If Edelgard wasn’t confused before, she was questioning her own sanity now. But before she could react, she felt Byleth’s hand forcefully grab her arm that was closest to her mouth.

“Professor, what are you-“ Edelgard started to protest before she felt Byleth lifting her sleeve and wrapping her teeth around her arm.

There was a sharp pain, and Edelgard cried out. It felt as if two needles had plunged into her skin and it hurt like hell. But it only hurt for a second before Edelgard started to feel a bit light headed. Suddenly, she felt relaxed.  
She stared down at her professor, watching blood dripping down from her arm into Byleth’s wanting mouth. Her professor licked her wound clean, eagerly drinking up her blood as if it was the sweetest drink she had ever tasted. And seeing her professor satiate her thirst like that made Edelgard feel a familiar strong emotion. Her lavender eyes followed Byleth’s tongue as Edelgard grew hotter and her sex grew wetter.  
She was loving the view when her professor abruptly stopped, quickly pulling away and turning her face as if she was suddenly disgusted with what she had done.

“You have to leave, right now!” Byleth commanded in the same tone she gave orders on the battlefield, yet Edelgard couldn’t move.

Her professor suddenly seemed a lot healthier, but her eyes were still looking like a beast’s. Edelgard looked down to see her wound of two punctures starting to quickly heal as her lightheadedness started to fade as well. Her arm had no visible blood, licked clean by Byleth’s mouth with only a faint trail of saliva covering it, and even the two small marks were disappearing from her skin.  
As Edelgard examined her arm in awe, Byleth moved, getting away from Edelgard and curling up in her bed after begging her student to leave one last time.

“My teacher, what are you?” Edelgard asked her, desperate to understand all of this. She tried to touch Byleth, but her professor shied away from her touch, backing away from her like a wounded animal.

“Edelgard, please” Byleth desperately cried out, “I don’t want to hurt you again. You have to leave before I hurt you.”

“Why would you hurt me?” Edelgard asked, moving closer to Byleth.

Edelgard moved closer, and Byleth tried to back away once again. But she could only back away so much before Edelgard had her trapped. Before Byleth could do anything about it, Edelgard had pinned her down on the bed.

“Cowering isn’t like you, my teacher. But I can’t let this slide, even if you’re my professor. So please, tell me why you did this and I’ll leave” Edelgard demanded, pinning Byleth down out of necessity but the act making her desire grow.

Byleth could have easily thrown Edelgard off of her, but she didn’t want to hurt her. That, and despite feeling better, she hadn’t regained her full strength yet. So Byleth sighed in defeat.

“I’m a demon” Byleth started, surprising Edelgard with her answer, “no one knows exactly what kind of monster I am, but I need fresh blood to survive. As a mercenary it was easy to hunt down animals, but here at the monastery everything is controlled and I can’t let people find out. My father has been offering his blood, but since lady Rhea sent him away for a long mission I’ve been thirsty and grown weaker for days…I don’t want to do this and hurt you, but I can’t control my thirst if you’re near…”

Edelgard noticed Byleth’s mouth starting to salivate and she understood that her professor needed more blood than what she had already taken.

“I’m not leaving, my teacher” Edelgard decided, “demon or not…if it’s blood you require to survive, I won’t let you perish!”

Byleth tried to stop Edelgard but it was too late. Edelgard took her glove off from her left hand, and held her hand out in front of Byleth’s mouth. Byleth licked her lips, and unable to resist, she bit down on Edelgard’s palm.  
The younger woman let out a yelp when the pain hit her, but as soon as that strange feeling of relaxation hit her again she couldn’t help but moan.  
As Byleth sucked on her skin, Edelgard stared intently. She started feeling excited again, and very much aroused. Somehow the second time was even worse than the first in that regard.  
She couldn’t help but lower her hips to meet Byleth’s pelvis, slightly and discreetly rubbing herself on Byleth as Byleth mindlessly licked and sucked on her hand for that sweet blood. Edelgard felt her heart race and her cheeks burn as her desire to do unspeakable things with her professor grew.

“My teacher…” Edelgard moaned, and Byleth stopped for a moment to stare at Edelgard’s lust filled eyes, “may I kiss you?”

Byleth’s cheeks burned red.  
She didn’t expect Edelgard to get off on something like this. But watching the younger woman above her made her clear of Edelgard’s aroused state. She nodded.  
Byleth pulled away from Edelgard’s hand, and the younger woman’s lips clashed onto hers almost instantly. They kissed passionately, Edelgard’s tongue begging for entrance so she could taste her own blood in Byleth’s mouth.

“It’s…an exquisite taste…” Edelgard commented once they pulled away, uttering a “thank you” before putting her bloodied hand back on Byleth’s mouth. 

Byleth quickly and eagerly got back to her previous task. When she finished, she released Edelgard’s hand and the younger woman pulled away.

“You cleaned me good” Edelgard softly laughed, as she examined her hand. Once again, the punctures were starting to fade just like the ones in her arm. There wasn’t a single trace of blood, and as soon as the marks faded it was as if nothing had happened.

Byleth, still under her and slightly embarrassed, apologized again.

“Please, my teacher, don’t apologize. I’m sure this condition is not your fault.”

Edelgard dipped down to kiss Byleth again. Byleth was surprised, but she didn’t pull away. She’d be lying if she said she wasn’t enjoying Edelgard’s attention, after all.

“You are so cute like this, my teacher…your fangs and your eyes are intimidating, but your demeanor is so soft…” Edelgard whispered close to Byleth’s ear, and Byleth was unable to suppress an embarrassing moan.

“Oh? Perhaps you feel the same desire I do…” Edelgard purred, “…if you consent, we can-“

Edelgard was interrupted by a hungry kiss from Byleth. She smiled internally as she kissed her professor back, her hands tugging at Byleth’s clothes in a hurry to undress the woman beneath her. As she kissed Byleth, her tongue traced her professor’s fangs.

“You usually don’t have teeth this sharp” Edelgard commented once she pulled away, “is it normal that they haven’t returned to normal?”

“I’m still a bit thirsty” Byleth confessed, embarrassed, “but I drank enough to control myself, I won’t hurt you again. I’ll drink more some other day if I manage to hunt down an animal or my father returns…”

Byleth felt Edelgard cup her cheeks, forcing her to stare at her beautiful lavender eyes.

“That won’t do, my teacher” Edelgard purred, “if you behave, I’ll let you drink more from me.”

“No, Edelgard, I don’t want to hurt you! That’s not necessary, I had enough to survive-“ before Byleth could finish, she felt Edelgard’s mouth in her throat. 

Edelgard bit down to leave her mark on Byleth, and Byleth moaned at the contact.

“Hush” Edelgard whispered, “be a good girl and let me take care of you…”

With that, Byleth fell silent.  
Edelgard worked on undoing Byleth’s armor, tossing the pieces aside as she undressed her. She was getting rid of Byleth’s underclothes when Byleth’s eyes focused on Edelgard’s neck. The way she was bent down over Byleth brought her delicious neck dangerously close to the professor’s mouth, and almost by instinct, Byleth moved to lick her skin there.

“Don’t even dare!” Edelgard warned, “if you want my blood, you’ll have to behave first.”

Byleth whined, and reluctantly moved her mouth away from Edelgard’s skin.  
But her protest didn’t last long, as she soon felt Edelgard’s fingers playing at her entrance.  
Byleth’s whines instantly turned to moans as Edelgard started playing with her clit. Edelgard’s gloved hand, the one that wasn’t touching Byleth’s sex, moved to softly caress Byleth’s cheek as Edelgard’s fingers entered the professor.

“Good girl” Edelgard praised the moaning mess of a woman underneath her, dipping down yet again to kiss her. The professor could only wrap her arms around Edelgard to pull her closer, crying out into Edelgard’s mouth as she started to near her orgasm.  
Her walls clenched around Edelgard’s fingers, and Byleth finally came.  
Edelgard merely removed them, licking them and tasting Byleth’s juices as the professor underneath her tried to recover her breath.  
Edelgard took in the sight of her beautiful professor naked, panting and absolutely flushed. She stared at Byleth’s mouth, slightly agape as she was still breathing heavily but salivating with her insatiable hunger. Almost in an instant, Edelgard knew what she wanted Byleth to do next.

“Will you eat me out, my Byleth?”

Byleth licked her lips before nodding.  
And that was all that Edelgard needed.  
She hurried to take her shorts off, her red tights and undergarments following them. As soon as she was naked from the waist down and had tossed her clothes aside, she straddled Byleth’s mouth. Byleth started by teasing Edelgard, her tongue running over the creamy skin of her thighs. 

“Don’t bite me” Edelgard commanded, a hand firmly gripping Byleth’s hair without hurting her but asserting that she was serious.

Byleth behaved, her tongue darting up instead to taste Edelgard’s already wet slit. As she ate Edelgard out, she could hear the woman above her making noise, moaning in absolute pleasure. Tasting her and hearing her made Byleth forget her thirst for blood. Soon, she was focused on pleasing Edelgard, her tongue lapping inside her as Edelgard thrust her sex into Byleth, her juices dripping onto her mouth. Riding Byleth like that, Edelgard didn’t last very long.  
She came on Byleth’s lips, and removed herself from Byleth. It took her a moment to catch her breath, but as soon as she did so, she got up from the bed. Byleth wondered where she was going before she saw Edelgard kneel to pick up her shorts. She assumed Edelgard was getting dressed to leave and sat up to talk to her, but instead Edelgard merely took a handkerchief out of her short’s pocket and returned to Byleth.  
Before Byleth could say anything, Edelgard was using it to clean her own juices off of the older woman’s mouth.

“As I promised, this is the part where I let you drink more of my blood” Edelgard told her as she cleaned Byleth’s lips, a faint flush across both hers and Byleth’s face.

“N-no Edelgard, it’s fine, I promise. I really don’t want you to faint or get hurt because of me, you don’t need to do this.”

“Please, my teacher, I seriously insist” Edelgard assured her, blushing, “I promise that I’m feeling fine; you haven’t taken that much blood to make me ill. Besides, I trust you. I know you won’t hurt me enough to leave me injured.”

Byleth tried to protest, but Edelgard moved to lay on the bed beside her and embrace her.

“I…I truly wish to help. And after what we did, it only feels right. So please, allow me to keep my promise…”

With that, Edelgard pulled her hair back, revealing her exposed neck. Byleth stared, unable to resist. She apologized and dug in, biting down on it. Once again, Edelgard felt a sharp pain that was soon replaced with a feeling of relaxation as Byleth licked and sucked on the punctures, drinking her blood.  
When she was done, she pulled back.  
Her fangs seemed to have retracted, giving her the appearance of having normal human teeth inside her mouth. Her eyes had lost their shine, her irises returning to their regular blue shade and her pupils returning to normal as well. She looked less pale now, and her body became warm again.

“Thank you, Edelgard” was all that Byleth could reply, her cheeks still red from everything they did. Yet Edelgard was even more embarrassed than her professor was.

“I want to assure you that I won’t tell anyone of your condition. And I promise to help you whenever you need me too. But…” Edelgard started, shyly, but trailed off.

“But you want us to have sex as payment for helping me?” Byleth tried to finish her sentence.

“What? No!” Edelgard let out, suddenly concerned “my teacher, I’m so sorry if I coerced you in any way…I didn’t mean to! I thought you wanted this as well, I would never-!”

Edelgard started to panic, but Byleth shushed her with a soft kiss.

“I’m sorry, I was trying to make a joke, but my face doesn’t help” Byleth explained once she pulled away from a petrified Edelgard, “everything I did was because I wanted to do, I would have stopped you if I didn’t. I just wish we had done this under different circumstances.”

Edelgard sighed.

“You scared me. I couldn’t live with myself knowing I hurt you, so please, never joke about that again.”

Byleth smiled.

“You really like me.”

“I do” Edelgard confessed, smiling in return upon seeing her professor smile, “I always hoped you liked me as well.”

“I do” Byleth answered honestly, “but doesn’t it bother you that I’m a monster?”

“You’re not a monster, Byleth” Edelgard assured her, “it’s just…a unique condition, that’s all. Besides, I don’t care. I like you for who you are as a person, regardless of everything…and I’d love to keep meeting you, if you want to as well.”

Byleth snuggling with her came as Edelgard’s answer.  
She murmured a quiet “yes” before drifting off to sleep, with Edelgard holding her close as she played with Byleth’s hair.

“Sleep well, my teacher. Your secret is safe with me.”


End file.
